A heat detector monitors the ambient thermal condition in the region where the heat detector is placed. A heat detector can be included as part of a smoke detector or operate as a stand alone device. The heat detector typically has a rate of rise capability that triggers an alarm whenever the ambient temperature change exceeds a predetermined rate and persists for a predetermined time. Certain heat detectors trigger an alarm also whenever the ambient temperature exceeds a fixed threshold, irrespective of the rate of thermal change.